The auditory capacities of listeners with sensorineural hearing loss due to cochlear pathology will be examined in several psychoacoustical investigations of auditory masking. Using the electrophysiological observation of the abnormal frequency response of single auditory nerve fibers of cats with damaged cochleas as a model for experimentation, psychophysical tuning curves in normal and impaired ears will be compared in the first experiment. Psychophysical tuning curves relate level of a tonal masker just sufficient to mask a probe of fixed frequency and intensity to frequency of the masker and have been shown in pilot work to provide a sensitive measure of the frequency selective properties of the auditory system in both normal and impaired ears. In a second experiment, the potentiating effects of auditory masking with sensorineural damage is assessed with a simple additive model in which the effects of the masker and the debilitating effects of the cohlear damage are assumed to summate linearly. Preliminary work has shown that hearing loss due to acoustic trauma can give rise to non-additivity (potentiation) of as much as 18 dB. In a second study, perfect additivity was obtained in an ear with uniform low frequency loss. Nonlinearities in the impaired ear will be assessed in the third study by mapping the amplitude and phase behavior of the combination tones, 2f1-f2 and f2-f1. In this effort, masked audiograms depicting the excitation pattern of the total masker will be the primary indicant of the nonlinearity. In all three studies, a broad range of frequencies and levels for the signal and masker will be investigated in order to adequately sample the frequency-intensity dimensions for each listener. The effects of background noise and nonsimultaneous presentation of signal and masker will be used to more fully explore the range of auditory processing available to listeners with impaired hearing.